There is the story of the bed bug. In the winter season the bed bug appears to be only skin, but in summer season as soon as it gets the opportunity of biting and sucking blood, it becomes fatty. Sometimes we may artificially renounce the world, but as soon as the opportunity of sucking blood is there, we turn again into a bed bug. Therefore it is said in the Bhagavad gita: daivi hy esa gunamayi / mama maya duratyaya / mam eva ye prapadyante / mayam etam taranti te [Bg. 7.14]. "This divine energy of Mine, consisting of the three modes of material nature, is difficult to overcome. But, those who have surrendered unto Me can easily cross beyond it.''
Letter to Karandhara das, 19 October, 1973